Note: Descriptions are shown in the official language in which they were submitted.
377~3
The present invention xel~tes -to optical smoke detectors. Such
detectars direct a beam o~ ligh~ into a dark chamber which is shielded in
as much as possible from ambient light. Air to be tested for the presence
of the smoke ~ill flow into the dark chamber and will scatter the light in
the beam to initiate an alarm signal.
In the past, various arrangements have been utilized to allow smoke
to enter a smoke detector. The United States patent to Steele et al 3,916,209
discloses forming the passages in a swirled shape so that air to be sampled
and tested will flow through narrowing passages towards a terminal convergence
point and then be diverted into a dark chamber which is disposed below the
convergence point. In the United States patent to Steele, No. 4,12~,29~,
November 7, 1978, the optical sensing zone is located in a dark chamber formed
by interior walls. Air to be tested enters through smoke entrances that are
formed circumferentially and screens are disposed in each smoke entrance to
prevent insects from enter mg the equipment and also reduce the passage of
light into the dark chamber.
According to a broad aspect of the present invention, there is pro-
vided an optical smoke detector comprising: a housing enclosing a dark
chamber; means for sensing smoke in the dark chamber; said housing including
wall means forming a plurality of spiralled passages extending from an outer
periphery to smoke ports opening into said dark chamber, the wall means ~orm-
ing smoke entrances extending substantially completely around the entire
periphery, the wall means on one side of each passage overlapping the wall
means on the other side of the passage so as to obstruct light Erom entering
the smoke port at the end of the passage.
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~ o~e specificalLy stated, the optical scanning detector includes
a centrally located dark chamber and an adjacent smoke sensor. A plurality
of walls extending from smoke entrances are disposed on the outer perimeter
of the detector to smoke ports that open directly into the dark chamber.
The walls cooperate to form passages of diminishing width Eor air to be
sampled to flow from the smoke entrances to the smoke ports. They are
arranged so that the entire perimeter of the smoke deteclor is free from
obstructions, save for the width of the walls, thereby allowing air to be
tested to enter throughout the entire periphery of the device. A screen is
disposed in ront of the smoke entrances to prevent insects Erom entering
the passages and El~ing into the dark chamber. The screen contacts the
walls only at their outer ends~ if at all, thereby allowing a substantially
unobstructed flow o air to be tested. Since the screening constitutes only
a negligible obstruction ln air flow, relative to the large sizes of the
smoke entrances that extend around the entire perimeter of the detector,
all air in the immediate area will
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flow through the passages and into the dark chamber.
DRAWINGS
Figure 1 is a top plan view of the optical smoke
detector. A portion of the cover of the detector is
shown in the view.
` Figure 2 is a cross sectional view taken along
the line 2-2 of Figure 1,
DESCRIPTION
The optical smoke detector of ~igures 1 and 2
- comprises a disk shaped base 1 on which is secured an
electronic circuit board 29 the circuit components
being omitted. Attached to the circuit board is an
optical block 3 containing a light emitting diode (LED)
~ and a photocell 6, ~ight from the I~D source 4 is
directed out a pas~a~e in the light block on a first
beam axis 7 to intersect a second axis 8 on which the
cell 6 views through a passage( to a smoke sensing zone
Z, Light is scattered by smoke in the sensing zone to
the cell 4, exciting the cel] to an alarm response if
the smoke exceeds a predetermined densi-ty,
The intersection zone ~ is located in a dark
chamber 5 from whiah light is excluded so far as is
possible while admitting smoke as freely as possible. The
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dark chamber is located between the optical block 3
and a cover 9 in the vertical dimension of ~igure 2
and within a molded plastic wall forming structure ll,
The wall forming structure comprises a circular disk
12 interrupted centrally by a rectangular opening 14
modified at two opposite sides by dished out portions
16, Depending from three sides of the rectangular opening
are flat walls 17 which fit closely around the optical
block and obstruct ambient light entry from the circuit
0 board side of the dark chamber, and whi~ support the
wall forming structure on the circuit board 2. A collar
30 covers the detector below the disk 12. It will be
understood that reference to the vertical and up and down
dimensions are with reference to the smoke detector as
lS shown ln the Figures and the detector may be installed
on a wall or on a ceiling with ~ertical and horizontal
dimensions reversed, Also while smoke entrances will be
described it should be understood that, depending on the
direction of smoke currents, entrances will at some times
be exits.
Of particular significance in the present invention
are the walls and screening extending from the upper
side of the disk 12 to ~he cover 9. A first s~ of
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circulax walls 18 defining the outer b~undary of the
dark chamber form smoke ports 19 openin~ into the
dark chamber, Preferably a baffle 21 is located inside
each port 19. ~rom the circulax walls 18 outwardly
spiralled walls 22 extend to an outer periphery of the
wall structure defined by a ring shaped screen 23,
The cover 9 over the dark chamber is supported
by and attached to the walls 18, 21 and 22 ex-tending
upwardly from the disk 12 of the wall forming s-tructure
11. ~he cover 9 and disk 12 have opposed annular grooves
29 and 32 which receive and positively position the ring
shaped screen 23 around the periphery of the detector~
The outer ends 24 of the spiralled walls terminate at
the periphery and adjacent outer ends 24 of the walLs
and foxm smoke entrances 26 at the periphery, Excluding
the negligible dimension of the outer ends 24 of the
spiralled walLs 22, these smoke entrances extend in four
quadrants completely, or substantially completely, around
the available smoke entry area at the periphery thus
maximizing the free entry of smoke -toward the dark chamber.
At the same time each spiralled wall 22, as extended
continuously by the circular walls 18, overlaps its
adjacent spiralled wall so that each adjacent wall pair
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forms an inwarlcy spiralling and converging passage 26
from each smoke entrance to a smoke port l9, there being
four such passages,
~y drawing a line from any spixalled wall outer
end 24 through the adjacent passage 26 to the inner smoke
port l9, it can be seen that direct light rays from the
smoke entrance are blocked by the wall structure,
Moreover, the wires of the screen 23 substantially
obstruct light rays entering each quadrant of the
screened periphery at an oblique angle obstructing
approach to each port l9, but at the same time afford
the maximum 360 area for radial entry of smoke into
the passages 26 leading to the dark chamber, Test data
indicate a substantial and significant increase in the
speed in which an alarm level ~ smoke will be detected
because of the maximized smoke entry characteristic
of the present invention together with the decreased
entry of ambient or external ligh~,
It should be understood that the present disclosure
is for the purpose of illustration only and that this
invention includes all modifications and equivalents
which fall within the scope ~ the appended claims.
As our invention~ we claim:
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